It has been proposed in many patents and articles (for example, U.S. Pat. Nos. 4,164,473; 4,176,073; 4,176,074; 4,192,757; 4,248,720; 4,201,683; 4,289,635; and 4,479,883) that oil soluble molybdenum is useful as a lubricant additive. In particular, molybdenum provides enhanced fuel economy in gasoline or diesel fueled engines, including both short and long term fuel economy (i.e., fuel economy retention properties). The prior proposals typically use molybdenum at levels greater than 350 ppm up to 2,000 ppm in the oils, which contain one or more detergents, anti-wear agents, dispersants, friction modifiers, and the like.
The present inventors have found that fuel economy properties can be improved using two different types of molybdenum additives in combination with an organic friction modifier, a calcium or magnesium overbased detergent and a zinc dihydrocarbyl dithiophosphate.